1. Field of the Invention
The field of the invention relates to medication delivery pens including dosage setting means.
2. Brief Description of the Related Art
A number of devices have been developed for administering insulin, drugs or other substances to persons and animals. As self administration of certain substances, such as insulin, is common, it is important that devices designed for self-administration be simple to operate, reliable and accurate.
U.S. Pat. No. 4,883,472 discloses an injection device which is capable of dispersing the contents of a pre filled cartridge by advancing the piston within the cartridge by a selected amount. A displacing sleeve is provided for axially displacing a gear element by a constant stroke. The sleeve is moved in the advancing direction against the force of a spring, and is moved back to a rest position by the spring. A threaded rod may be axially advanced with respect to the gear element in order to set the desired dosage. The rod engages the cartridge piston when the sleeve is advanced, thereby advancing the piston by a selected distance corresponding to the selected dosage.
U.S. Pat. No. 4,865,591 discloses another injection device which, unlike that disclosed in U.S. Pat. No. 4,883,472, controls the dosage by allowing the stroke of a drive member to be varied. The distance traveled by the drive member corresponds to that traveled by the piston within an insulin cartridge. The dosage is displayed through a port in the body of the pen. The port is positioned adjacent to a scale including indicia corresponding to dosage units.
U.S. Pat. No. 4,973,318 discloses another injection device in which the dosage administered corresponds to the distance traveled by the actuating member. A coarse dosage indicator is centrally located on the device, and provides an indication of smaller dosage units.
U.S. Pat. No. 5,017,190 discloses an injection device including a circumferential measuring scale which provides an indication of the individual steps of a ratchet as adjustment means are turned. A longitudinal measuring scale is provided on a piston rod and indicates the dosage amount.